The present invention relates to a dot crawling interference elimination device and a color subcarrier vertical correlation detection device therefor which are used to eliminate a color signal that mixes into a luminance signal when a non-standard signal which does not meet the standards of the NTSC system or the PAL system is Y/C separated, in a television receiver having a motion-adaptive Y/C separation function.
There are various problems occurring in a television receiver, such as dot crawling interference and cross color interference which occur due to multiplexing of the frequency of a color signal with the frequency of a luminance signal, line flicker which occurs due to interlace scanning, and deterioration of picture quality which occurs due to reduction in vertical resolution, etc. In order to solve these problems, frame memories and digital signal processing techniques have been used in recent years, thereby to improve the quality of the picture in a television receiver. These methods introduce processing techniques such as a three dimensional Y/C separation which utilizes correlation of time directions of video signals and a sequential scanning converter.
Based on these high picture-quality processing techniques, it is a pre-condition that the input television signals are completely based on the NTSC system or the PAL system. In other words, the signals used for these systems have a predetermined relationship of frequencies including a color subcarrier frequency, a horizontal scanning frequency and a vertical scanning frequency (hereinafter referred to as a standard signal). For example, in carrying out a Y/C separation of a still image, if a color subcarrier frequency, a horizontal scanning frequency and a vertical scanning frequency are in a predetermined frequency relationship, a frame comb filter becomes valid which utilizes a correlation of time base direction of a video signal to separate a luminance signal from a color signal. However, if a frame comb filter is used for home VCRs or personal computers which does not have a predetermined relationship of a color subcarrier frequency, a horizontal scanning frequency and a vertical scanning frequency, a Y/C separation cannot be performed normally so that this causes a problem of deterioration in the picture quality.
In order to solve the above problem dot crawling interference elimination devices have been proposed, according to which a non-standard characteristic of an input video signal is detected by utilizing inter-frame correlation of a color burst signal, and a frame comb filter and a line comb filter are changed over therebetween in accordance with a result of the detection, and further, a notch filter for a color subcarrier signal band is applied to a luminance signal resulting from the Y/C separation.
Description will be made of a preceding dot crawling interference elimination device with reference to the accompanying drawings.
FIG. 11 is a block diagram of a preceding dot crawling interference elimination device. In FIG. 11, 101 designates an input terminal, 102 a non-standard signal detection circuit, 103 an image motion detection circuit, 104 a line comb filter, 105 a frame comb filter, 106 a line comb filter and frame comb filter change-over circuit, 107 an OR circuit, 108 a color subcarrier band pass filter, 109 a color subcarrier band notch filter, 110 a notch filter change-over circuit, 111 a subtractor, and 112 an output terminal.
Referring to FIG. 11, when a non-standard signal is detected by the detection circuit 102 or when a motion image is detected by the detection circuit 103, the change-over circuit 106 selects the line comb filter 104 so that a video signal which is applied to the input terminal 101 is Y/C separated by the line comb filter. When an input video signal is non-standard, the luminance signal component can not be completely separated from the video by the line comb filter. Therefore, the separated luminance signal containing the color subcarrier component attenuated by the notch filter 109 in the next step, is selected by the notch filter change-over circuit 110 and supplied to the output terminal 112.
The non-standard detection circuit 102 detects an inter-frame correlation of the color burst signal of the input video signal, and makes a decision whether the input signal is a non-standard signal or not, on the basis of a result of the detection.
According to the above-described arrangement, however, a non-standard state of an input video signal is judged based on only the inter-frame correlation of a color burst signal. Therefore, there is a problem of an incomplete or erroneous detection of the non-standard signal when the relation between the color subcarrier frequency and the vertical scanning frequency meets the relation in a standard signal, even if the color subcarrier frequency does not have a normal relation with the horizontal scanning frequency. As a result, there arises such a situation that a signal which should be Y/C separated by a line comb filter is separated by a frame comb filter. Further, there is a problem that a color signal component which has been mixed into a luminance signal component that is a result of such an erroneous Y/C separation processing, that is, a dot crawling component, does not subject to the processing attenuating the same by a post-stage notch filter, so that a dot crawling component remains in the luminance signal component.